JP2023098879A - Fan silencing system - Google Patents

Abstract

To provide a fan silencing system capable of muffling discrete, multiple-frequency, narrow-band sounds generated by a fan while maintaining the fan's airflow.SOLUTION: An embodiment of the present invention comprises a fan and an acoustic resonance structure, and the acoustic resonance structure is located within a near-field region of a sound generated by the fan.SELECTED DRAWING: Figure 1

Description

The present invention relates to a fan silencer system.

Fans are known to generate a very narrow band and strong sound at frequencies corresponding to the number of blades and the number of revolutions of the fan, which poses a problem as noise. In order to reduce such noise, it has been proposed to place a muffler in the path of the air flow (wind) generated by the fan.

For example, Patent Literature 1 discloses a noise reduction device for a device that includes a heat source such as a light source lamp unit and an exhaust fan for exhausting heat from the heat source, wherein a member for guiding the exhaust air of the exhaust fan is It is sealed from the air outflow side to the outside of the equipment, and on the peripheral wall facing the ventilation path of the air guide member, an elastic membrane that can be vibrated by the sound wave generated by the exhaust fan is placed so as to at least collide with the exhaust air flow and in the exhaust direction. describes a muffler in which an air chamber is formed behind the elastic membrane body and arranged at a position where the air flow is not blocked. The noise reduction device described in Patent Document 1 converts sound energy into vibration energy by applying an air flow (wind) generated by a fan to an elastic membrane to vibrate the elastic membrane, thereby muting the sound.

Also, in order to reduce narrow-band noise, it has been proposed to use a resonance muffler.
For example, Patent Document 2 discloses an impeller having a plurality of blades, an air guide having a plurality of stationary blades arranged around the impeller, an electric motor driving a rotating shaft to which the impeller is fixed, and an airflow to the impeller. A substantially cylindrical fan case with an intake port in the center and an exhaust port on the side, which contains the impeller and the air guide and is fixed to the motor, and a fan with an exhaust port that encloses the entire motor. A soundproof cylinder airtightly fixed to the case, a substantially cylindrical sound-absorbing means having a recess having a predetermined width and depth on the circumference and provided at a predetermined place on the surface of the motor, and an open end face of the recess of the sound-absorbing means. An electric blower is described that includes a flexible membrane portion provided on the . This patent document 2 describes that the sound of a specific frequency determined according to the depth of the concave portion resonates to muffle the sound.

Japanese Patent Application Laid-Open No. 2001-142148 Japanese Patent Application Laid-Open No. 2008-036065

As in Japanese Patent Laid-Open No. 2002-100000, in the case of a configuration in which air flow (wind) generated by a fan is applied to an elastic membrane to vibrate the elastic membrane to muffle noise, an elastic membrane is used to strongly vibrate the elastic membrane. Since it is necessary to place the fan so that the wind directly hits the body, it should be placed so as to partially block the airflow path generated by the fan. Therefore, there is a problem that a large pressure loss is caused in the fan and the air volume is reduced.
Further, in Patent Document 1, since a large wind pressure is applied to the elastic membrane, the characteristics of the elastic membrane change when the air volume and wind pressure of the fan change. Therefore, the resonance effect formed by the properties of the elastic membrane and the back air layer cannot be used. Therefore, it is difficult to obtain a large noise reduction effect for the fan because it is not possible to obtain a large noise reduction effect by targeting the sound of a specific frequency generated by the rotation of the fan.

Fan noise is known to occur discretely at a plurality of frequencies depending on the number of blades and the number of revolutions. A resonance muffler such as that of Patent Document 2 muffles sounds of a single frequency that matches the resonance frequency of the resonance muffler, and has a low muffling effect on sounds in other frequency bands. . Therefore, there is a problem that it is difficult to silence sounds of a plurality of frequencies that occur discretely.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a fan silencing system that is capable of silencing narrow-band sounds of a plurality of discrete frequencies generated by the fan while ensuring the air volume of the fan. The task is to provide

The present invention solves the problems with the following configurations.

[1] having a fan and an acoustic resonance structure,
A fan noise reduction system in which the acoustic resonance structure is placed in the near-field area of the sound generated by the fan.
[2] The fan muffling system according to [1], wherein the resonance frequency of the acoustic resonance structure matches at least one frequency of discrete frequency sound caused by rotation of fan blades.
[3] Described in [1] or [2], wherein the area where the acoustic resonance structure overlaps the air outlet when viewed from the direction perpendicular to the air outlet of the fan is 50% or less of the area of the air outlet. fan silencer system.
[4] The fan muffling system according to any one of [1] to [3], wherein the acoustic resonance structure constitutes a part of the wall surface of the ventilation passage connected to the fan.
[5] The fan muffling system according to any one of [1] to [4], wherein the surface of the acoustic resonance structure having the vibrator is arranged parallel to the axis perpendicular to the air outlet of the fan.
[6] The fan muffling system according to any one of [1] to [5], which has a sound-transmitting windbreak member on the surface of the acoustic resonance structure provided with the vibrating body.
[7] The fan muffling system according to any one of [1] to [6], wherein the acoustic resonance structure is in contact with the fan.
[8] The fan muffling system according to [7], wherein the acoustic resonance structure is in contact with the fan via a vibration isolating member.
[9] having a plurality of acoustic resonance structures with different resonance frequencies;
The fan muffling system according to any one of [1] to [8], wherein the acoustic resonance structure with a high resonance frequency is arranged closer to the fan than the acoustic resonance structure with a low resonance frequency.
[10] The fan muffling system according to any one of [1] to [9], in which the acoustic resonance structure is arranged only downstream of the fan in the blowing direction of the fan.
[11] The fan muffling system according to any one of [1] to [9], wherein the acoustic resonance structures are arranged upstream and downstream of the fan in the air blowing direction of the fan.
[12] The acoustic resonance structure is a membrane-type resonance structure having a membrane with a fixed peripheral edge and supported so that the membrane can vibrate, and a back space formed on one side of the membrane [ 1] The fan muffling system according to any one of [11].
[13] The fan muffling system according to [12], wherein the membrane-type resonance structure has a through hole that communicates the back space with the outside.
[14] The fan noise reduction system according to any one of [1] to [13], wherein the fan is an axial fan.

Advantageous Effects of Invention According to the present invention, it is possible to provide a fan silencing system capable of silencing narrow-band sounds of a plurality of discrete frequencies generated by a fan while ensuring the air volume of the fan.

1 is a perspective view schematically showing an example of a fan noise reduction system of the present invention; FIG. FIG. 2 is a view of the fan muffling system of FIG. 1 viewed from direction A; 3 is a cross-sectional view of FIG. 2; FIG. FIG. 4 is a cross-sectional view schematically showing another example of the fan noise reduction system of the present invention; FIG. 4 is a cross-sectional view schematically showing another example of the fan noise reduction system of the present invention; FIG. 4 is a cross-sectional view schematically showing another example of the fan noise reduction system of the present invention; FIG. 4 is a cross-sectional view schematically showing another example of the fan noise reduction system of the present invention; FIG. 4 is a cross-sectional view schematically showing another example of the fan noise reduction system of the present invention; FIG. 4 is a cross-sectional view schematically showing another example of the fan noise reduction system of the present invention; FIG. 4 is a cross-sectional view schematically showing another example of the fan noise reduction system of the present invention; FIG. 4 is a cross-sectional view schematically showing another example of the fan noise reduction system of the present invention; FIG. 4 is a cross-sectional view schematically showing another example of the fan noise reduction system of the present invention; 3 is a diagram schematically showing the configuration of Comparative Example 1. FIG. 4 is a graph showing the relationship between frequency and measured sound volume; 4 is a graph showing the relationship between frequency and measured sound volume; 4 is a graph showing the relationship between frequency and measured sound volume; FIG. 10 is a diagram schematically showing the configuration of Comparative Example 2; It is a graph showing the relationship between frequency and silencing volume. 4 is a graph showing the relationship between frequency and measured sound volume; 4 is a graph showing the relationship between frequency and measured sound volume; 4 is a graph showing the relationship between frequency and measured sound volume; 4 is a graph showing the relationship between frequency and measured sound volume; It is a graph showing the relationship between frequency and silencing volume. 4 is a graph showing the relationship between frequency and measured sound volume; It is a graph showing the relationship between current and wind speed. FIG. 11 is a diagram schematically showing the configuration of Example 5; 4 is a graph showing the relationship between frequency and measured sound volume; 4 is a graph showing the relationship between frequency and measured sound volume; 4 is a graph showing the relationship between frequency and measured sound volume; 4 is a graph showing the relationship between frequency and measured sound volume; FIG. 11 is a diagram schematically showing the configuration of Comparative Example 7; FIG. 12 is a diagram schematically showing the configuration of Example 9; 4 is a graph showing the relationship between frequency and measured sound volume;

The present invention will be described in detail below.
The description of the constituent elements described below is based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.
In this specification, a numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.
Further, in this specification, the terms "perpendicular", "parallel" and "perpendicular" shall include the range of error that is permissible in the technical field to which the present invention belongs. For example, "parallel" means within a range of less than ±10° with respect to strict orthogonality, and the error with respect to strict orthogonality is preferably 3° or less. In addition, it means that the angle is within a range of less than ±10° with respect to the exact angle.
As used herein, the terms “same” and “match” shall include the margin of error generally accepted in the technical field.

[Fan silence system]
The fan silencer system of the present invention is
having a fan and an acoustic resonance structure;
An acoustic resonance structure is a fan muffling system located within the near-field region of the sound generated by the fan.

The near-field region of the sound generated by the fan is the region where the sound waves are in the near-field state. The state in which the sound wave is in the near field is as follows.
The propagation direction and strength of sound waves generated from a sound source will eventually be determined by differences in attenuation for each wavenumber and spatial constraints (duct walls, curvature of flow paths, etc.). However, a sound wave generated from a sound source is not subject to the effects of the above attenuation and restrictions immediately after the sound wave is generated, and has amplitude over a wide range of wavenumbers, including high wavenumber components that cannot propagate over long distances. After this sound wave propagates over a certain distance, it becomes like a plane wave and its directionality is determined. The state immediately after sound waves are generated from the sound source is called the "near field" state. Therefore, the area near the sound source that satisfies the above conditions is defined as the near-field area.
It is known from the wave theory that wave number components that cannot propagate farther cannot propagate in this region after about λ/4 is propagated.
Therefore, in the present invention, the fan, which is the sound source, generates sound from the blades of the fan, so the near-field region is the region at a distance of less than λ/4 from the blades of the fan. Note that when the fan is arranged in the flow channel, the near-field region is a region along the flow channel whose distance from the fan is less than λ/4.

The sound in the near-field state (hereinafter also referred to as the near-field sound) is the sound emitted from the sound source that has a higher wave number than the propagating sound wave and cannot propagate far (sound speed c, frequency f When the wavenumber k>2π×f/c), it exists so as to spatially cling to the sound source. Specifically, in the wave equation that acoustic propagation follows, sound components with high wavenumbers where k>2π×f/c propagate farther than the sound source because the wave amplitude decays exponentially with distance. However, since the influence of attenuation is small in the near-field region, such high-wavenumber sound is localized only around the sound source as near-field sound, being mixed with the sound source.

In the fan noise reduction system of the present invention, by arranging the acoustic resonance structure in the near-field region, the following two interactions are generated with respect to the near-field sound within the near-field region, thereby obtaining a noise reduction effect. it is conceivable that.
The first interaction mechanism is as follows.
High-wavenumber sound waves of near-field sound are characterized by a small spatial wave size (reciprocal of wavenumber). As such, spatially local interaction can be achieved for acoustic resonant structures located near the sound source. Specifically, the sound pressure is locally applied only to a small portion of the acoustic resonance structure. A nonlinear effect is likely to occur in the acoustic resonance structure by causing such a local interaction in the acoustic resonance structure, which is difficult for sound waves of a wavenumber that propagates over a long distance. As for the first interaction mechanism, it is presumed that this non-linear effect also acts on sounds of frequencies other than the targeted silencing frequency (resonance frequency) of the acoustic resonance structure.

The second interaction mechanism can be presumed to be the effect of suppressing the generation of sound waves from the sound source by the sound reflected by the acoustic resonance structure and returning to the sound source position.
As the fan rotates, the blades cut through the air, creating microfluidic vortices in the air around the blades. The sound generated by the deformation of the vortex at the edge of the blade is the mechanism by which the sound (aerodynamic sound) generated by the fan is generated. By arranging the acoustic resonance structure near the sound source, the sound generated from the sound source is reflected by the acoustic resonance structure, the reflected sound propagates to the sound source, and interferes with the sound generated from the sound source. As a result of this interference, the sound pressure at the sound source location is reduced.
As an effect at this time, the sound pressure at the position of the sound source is lowered, and the amount of sound emitted from the sound source is reduced. This greatly reduces the radiated sound volume.
Furthermore, it is highly possible that not only the process of producing sound from the sound source, but also the generation of the sound source itself, and in the case of this fan, the generation of the micro-vortices themselves can be suppressed. Acoustic resonant structures located in the near-field region interact not only with far-propagating sound waves emanating from a sound source, but also with near-field sounds that have a high wave number and remain near the source. By strongly interacting with the acoustic resonance structure for this near-field sound, the wave number mode of the sound emitted from the acoustic vortex is biased toward the near-field sound, which is sound that does not propagate far, and the reflection due to this interaction causes the position of the sound source to change. The sound pressure is reduced even in the near field, and the amount of generation of micro vortices that act as a sound source is extremely suppressed.
On the other hand, in the acoustic resonance structure arranged in the far field, since the sound pressure at the sound source position does not decrease at the near-field wavenumber, the generation of the micro vortex that becomes the sound source itself cannot be suppressed much. Therefore, when the acoustic resonance structure is arranged in a near-field region capable of covering the wavenumbers of sound waves from low wavenumbers to near-field sound wavenumbers, the amount of generation of minute vortices that serve as sound sources is extremely small.
By reducing the amount of micro-vortices that generate a sound source, it is possible to reduce not only the frequency of the acoustic resonance structure, but also the aerodynamic noise of other frequencies. In particular, the peak sound of the fan emits a strong sound because the phases of the sound emitted from the minute vortices from each blade are aligned, creating a constructive interference effect. At this time, since the energy is proportional to the square of the number of sound sources, when the number of minute eddies, which are sound sources, decreases, the energy of the emitted sound decreases in accordance with the square. Therefore, it is likely to be greatly affected by the effect of reducing sound when the amount of minute eddies generated is reduced. Therefore, a selective silencing effect appears for a plurality of peak sounds. The effect of suppressing a plurality of discrete frequency sounds in the present invention is considered to be caused mainly by the reduction in the number of sound sources by the second mechanism and the associated peak sound suppression effect.
In addition, the noise called broadband noise (turbulent flow noise) other than the fan peak noise is generated after the phases of the sound sources of the blades are different and the phases of each sound source are different, and the number of sound sources is reduced. However, it is thought that the amount of noise is not significantly reduced, resulting in selective suppression of only the peak sound.

Such an effect is known in the field of optics, for example, JR Lakowicz et. ) shows the distance between the metal particle and the fluorescent particle, the emission intensity, the lifetime of the light source, and the production rate. It is conceivable that the same thing occurs with sound waves and sound sources.
When the acoustic resonance structure is in the near-field region, the distance to the sound source is less than λ/4 at maximum, so the phase change of the sound wave due to propagation is small. On the other hand, the phase of the sound wave is inverted (phase change of π) by being reflected by the acoustic resonance structure. Therefore, the sound generated from the sound source and the sound reflected by the acoustic resonance structure and returned to the sound source interfere with each other in opposite phases because their phase shifts are almost reversed. Therefore, the two sounds cancel each other out at the sound source position, producing a silencing effect at the sound source position.

As described above, in the fan noise reduction system of the present invention, by placing the acoustic resonance structure in the near-field region, the spatially localized sound peculiar to the near-field sound produces a nonlinear effect due to local interaction. and a mechanism that suppresses the generation of fluid eddies, which are the sound source, by reducing the sound pressure at the sound source position. Thus, the silencing effect can be obtained in a wide frequency band regardless of the resonance frequency of the acoustic resonance structure. Therefore, a silencing effect can be obtained for sounds of a plurality of discrete frequencies (hereinafter also referred to as discrete frequency sounds) generated by the fan.

Also, the mechanism of the above two interactions is the effect of the interaction between the sound source (sound wave) and the acoustic resonance structure, which are caused by arranging the acoustic resonance structure in the near-field region. Thus, the wind flow is irrelevant, so there is no need to position the acoustic resonance structure in such a way that the wind directly impinges on the acoustic resonance structure. That is, it is not necessary to arrange the acoustic resonance structure so as to partially block the airflow path of the airflow generated by the fan. Therefore, it is possible to suppress the noise generated by the fan while ensuring the air volume of the fan.

Here, as described above, the near-field region is the region whose distance from the sound source is less than λ/4. Therefore, the size of the near-field region differs depending on the wavelength (frequency) of the sound wave.
In the present invention, when the resonance frequency of the acoustic resonance structure is fr (the lowest order if there are multiple resonances), the wavelength is λ, and the region less than λ/4 from the fan sound source is the near-field region. do.

Note that at least a part of the acoustic resonance structure is preferably arranged in a region with a distance of λ/6 from the fan (sound source), and is arranged in a region with a distance of λ/8 from the fan (sound source) in order to improve the silencing effect. is more preferable. In the second mechanism described above, the closer the distance between the sound source and the acoustic resonance structure, the smaller the phase change in the process of being reflected by the acoustic resonance structure and returning to the sound source. The silencing effect due to is higher.

In the present invention, the acoustic resonance structure is one that resonates with sound waves at its resonance frequency to produce a silencing effect. Various structures can be selected as long as they cause a resonance phenomenon. For example, typical acoustic resonance structures include a membrane-type resonance structure, a Helmholtz resonance structure, and an air column resonance structure. Each acoustic resonance structure will be described in detail later.

The configuration of the fan noise reduction system of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic perspective view showing an example of a preferred embodiment of the fan noise reduction system of the present invention. FIG. 2 is a front view of FIG. 1 viewed from direction A. FIG. 3 is a cross-sectional view of FIG. 2. FIG. In addition, in FIG. 2, the acoustic resonance structure is shown in cross section. 2 and 3, illustration of the rotor of the fan and the like is omitted, and only the outer shape and the blower port are shown.

The fan muffling system 10 shown in FIGS. 1-3 has an axial fan 12a and a membrane resonance structure 30a.

The axial fan 12a is basically a well-known axial fan, and rotates a rotor having a plurality of blades to give kinetic energy to the gas and blow the gas in the axial direction.
Specifically, the axial fan 12a includes a casing 16, a motor (not shown) attached to the casing 16, and a shaft portion 20 attached to and rotated by the motor, and protrudes radially outward of the shaft portion 20. It has a rotor 18 with vanes 22 formed therein.
In the following description, the rotation axis of shaft portion 20 (rotor 18) is simply referred to as "rotation shaft", and the radial direction of shaft portion 20 (rotor 18) is simply referred to as "radial direction".

The motor is a general electric motor, and rotates the rotor 18 .

A shaft portion 20 of the rotor 18 has a substantially cylindrical shape, and one bottom side thereof is attached to the rotating shaft of the motor, and is rotated by the motor.
The blades 22 are formed on the peripheral surface of the shaft portion 20 so as to protrude radially outward from the peripheral surface. Also, the rotor 18 has a plurality of blades 22 , and the plurality of blades 22 are arranged in the circumferential direction of the peripheral surface of the shaft portion 20 . In the example shown in FIG. 1, the rotor 18 is configured to have four blades 22, but is not limited to this, and may have a plurality of blades 22. FIG. Also, although the number of frames of the casing 16 is four in the drawing, the number of frames is not limited to this.
Further, the shape of the blades 22 can be various shapes used in conventionally known axial fans.

The axial fan 12a generates an air current (wind) in the rotation axis direction by rotating a rotor 18 having blades 22 by a motor. The flow direction of the airflow is not limited, and the airflow may flow from the side of the motor in the direction opposite to the motor, or may flow from the side opposite to the motor in the direction of the rotation shaft.

The casing 16 has a fixed motor and radially surrounds a rotatable rotor 18 (blades 22).
The thickness of the casing 16 in the rotation axis direction is thicker than the thickness of the blades 22 and the shaft portion 20 so as to protect the rotor 18 from the outside.

The casing 16 has a blower opening 16a that opens in the direction of the rotation axis, and a rotor 18 is arranged in the blower opening 16a. When the rotor 18 having the blades 22 rotates, the air is sucked from one opening side of the blower port 16a and air is sent from the other opening side. That is, the airflow (wind) generated by the rotation of the rotor 18 is sent in the rotation axis direction.

The thickness of the casing 16 protects the rotor 18 from the outside, suppresses the flow of air in the radial direction among the air flows generated by the rotation of the rotor 18, and increases the air volume in the direction of the rotation axis. If possible, the thickness should be about 1.01 to 3.00 times the thickness of the blades 22 and/or the shaft portion 20 .

The axial fan 12a may further have various configurations of known axial fans.
For example, in the example shown in FIG. 1, the axial fan 12a has holes into which fastening members such as screws are inserted when fixing the axial fan 12a to various devices.

The membrane-type resonance structure 30a dampens discrete frequency sounds generated by the axial fan 12a.
The membrane-type resonance structure 30a has a frame 32 and a membrane 34, and has a back space 35 surrounded by the frame 32 and the membrane 34. The membrane-type resonance structure 30a is supported by the frame 32 so as to vibrate. Resonance occurs when the membrane 34 vibrates.

In the example shown in FIGS. 1 to 3, the frame 32 has a rectangular parallelepiped shape with an opening having a bottom surface on one side. That is, the frame 32 has a bottomed square cylinder shape with one side open.
The film 34 is a film-like member that covers the opening surface of the frame 32 where the opening is formed, and has its peripheral portion fixed to the frame 32 so that it can vibrate.
A rear space 35 surrounded by the frame 32 and the film 34 is formed on the rear side of the film 34 (the side of the frame 32 ). In the examples shown in FIGS. 1-3, the back space is a closed closed space.

In the examples shown in FIGS. 1 to 3, the membrane resonance structure 30a is arranged downstream of the axial flow fan 12a in the blowing direction. Further, the membrane-type resonance structure 30a is positioned so as not to block the air blown by the axial fan 12a (air blow port 16a). are placed. The membrane resonance structure 30a is arranged such that the membrane 34 is parallel to the rotation axis direction (the X direction in FIG. 3) of the axial flow fan 12a and the membrane 34 faces the rotation axis side.

Here, conventionally, when an acoustic resonance structure such as a membrane type resonance structure is used for muffling, the resonance frequency of the acoustic resonance structure is matched with the frequency of the sound to be muffled, and the resonance phenomenon is used to suppress the sound of this frequency. mute the Therefore, there is a problem that the effect of silencing sounds in other frequency bands is low, and it is difficult to silence a plurality of discrete frequency sounds.

On the other hand, in the fan noise reduction system of the present invention, the film-type resonance structure 30a is arranged in the near-field region of the sound generated by the fan, thereby generating the above-mentioned two interaction mechanisms and A plurality of discrete frequency sounds generated by the fan 12a can be silenced.
At this time, at least part of the vibratable portion of the membrane 34 needs to exist within the near-field region, and more preferably, the position of the center of gravity of the vibratable portion of the membrane 34 needs to exist within the near-field region. becomes.

Here, in the fan noise reduction system of the present invention, there is no particular limitation on the resonance frequency of the membrane-type resonance structure 30a (acoustic resonance structure).
In addition, in order to effectively utilize the silencing effect of the original resonance of the acoustic resonance structure, the resonance frequency of the acoustic resonance structure is desirably within the audible range (20-20000 Hz), and should be in the range of 100-16000 Hz. is more desirable.
The resonant frequency of the membrane-type resonant structure 30a (acoustic resonant structure) preferably corresponds to at least one frequency of discrete frequency sounds caused by the rotation of the fan blades. As a result, among discrete frequency sounds, the silencing effect can be enhanced at frequencies that match the resonance frequency of the acoustic resonance structure.
For example, the resonance frequency of the acoustic resonance structure preferably corresponds to the discrete frequency sound having the highest sound pressure level, more specifically, the highest A-weighted sound pressure level among the discrete frequency sounds. As a result, it is possible to effectively muffle the discrete frequency sound that contributes greatly to the noise of the fan.
Further, it is also preferable that the resonance frequency of the acoustic resonance structure matches the sound on the lowest frequency side among the plurality of discrete frequency sounds. Since it is difficult to muffle low-frequency sounds with ordinary sound-deadening materials, it is possible to selectively muffle low-frequency sounds by using resonance effects and then combine them with other sound-deadening materials.
In the present invention, the expression that the resonance frequency of the acoustic resonance structure matches one of the discrete frequency sounds of the fan means that the resonance frequency of the acoustic resonance structure is one of the discrete frequency sounds of the fan. The range shall be within ±10%.

In the case of an axial fan, if the number of rotations is z (rps) and the number of blades is N, a strong sound (discrete frequency sound) is generated.
The resonance frequency of the membrane-type resonance structure is determined by the size of the membrane 34 (the size of the vibration surface, that is, the size of the opening of the frame 32), thickness, hardness, and the like. Therefore, by adjusting the size, thickness, hardness, etc. of the film 34, the resonance frequency of the film-type resonance structure can be appropriately set.

Further, as described above, the membrane-type resonance structure 30 a has the back space 35 on the back side of the membrane 34 . Since the back space 35 is closed, sound absorption occurs due to interaction between membrane vibration and the back space.
Specifically, membrane vibration has a frequency band of fundamental vibration mode and higher-order vibration mode, which are determined by the conditions of the membrane (thickness, hardness, size, fixing method, etc.). The thickness of the back space or the like determines whether it is excited and contributes to sound absorption. When the thickness of the back space is thin, qualitatively, the effect of hardening the back space is produced, so that higher-order vibration modes of membrane vibration are likely to be excited.

In addition, in the examples shown in FIGS. 1 to 3, the back space 35 of the membrane-type resonance structure 30a is a closed space completely surrounded by the frame 32 and the membrane 34, but is not limited to this. It is sufficient if the space is substantially partitioned so that the flow of air is blocked, and the membrane 34 or the frame 32 may have a partial opening in addition to the completely closed space. In such a form having an opening in a part, the gas in the back space expands or contracts due to temperature change, tension is applied to the film 34, and the hardness of the film 34 changes, resulting in a change in sound absorption characteristics. It is preferable in that it can prevent
By forming a through hole in the membrane 34, airborne sound propagation occurs. This changes the acoustic impedance of membrane 34 . Also, the through holes reduce the mass of the membrane 34 . These can control the resonance frequency of the membrane-type resonance structure 30a.
There is no particular limitation on the positions where the through holes are formed.

The thickness of the membrane 34 is preferably less than 100 μm, more preferably 70 μm or less, even more preferably 50 μm or less. In addition, when the thickness of the film 34 is not uniform, the average value may be within the above range.
On the other hand, if the thickness of the film is too thin, it becomes difficult to handle. The film thickness is preferably 1 μm or more, more preferably 5 μm or more.
The Young's modulus of the membrane 34 is preferably 1000 Pa to 1000 GPa, more preferably 10000 Pa to 500 GPa, and most preferably 1 MPa to 300 GPa.
The density of membrane 34 is preferably between 10 kg/m 3 and 30,000 kg/m 3 , more preferably between 100 kg/m 3 and 20,000 kg/m 3 , and most preferably between 500 kg/m 3 and 10,000 kg/m 3 .

The thickness of the back space 35 (the thickness in the direction perpendicular to the surface of the film 34) is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 3 mm or less.
In addition, when the thickness of the back space 35 is not uniform, the average value may be within the above range.

In addition, in the examples shown in FIGS. 1 to 3, the shape of the membrane-type resonance structure 30a seen from the direction perpendicular to the surface of the membrane 34, that is, the shape of the vibration region of the membrane 34 is square, but is limited to this. It may have a circular shape, a polygonal shape such as a triangular shape, an elliptical shape, or the like.

In the fan silencer system of the present invention, as described above, the effect is due to the interaction between the sound source (sound wave) and the acoustic resonance structure due to the placement of the acoustic resonance structure in the near-field region. The effect of silencing can be obtained even if it is not arranged so that the wind hits directly. From the viewpoint of securing the air volume of the fan, the acoustic resonance structure is preferably arranged so as not to block the airflow path of the airflow generated by the fan.
Specifically, the overlapping area of the acoustic resonance structure and the air outlet when viewed from the direction perpendicular to the air outlet of the fan is preferably 50% or less, preferably 10%, of the area of the air outlet. is more preferably less than or equal to, and even more preferably 0%, ie no overlap, as shown in FIG.
Moreover, when the acoustic resonance structure and the air blowing port overlap, it is desirable to have a structure such as attaching a slope-like structure to smoothly flow the air and suppress the generation of wind noise.

Moreover, it is preferable that the surface of the acoustic resonance structure having the vibrator is arranged parallel to the axis perpendicular to the air outlet of the fan.
In the example shown in FIG. 2, the membrane 34 is the vibrating body of the membrane resonance structure 30a, and the plane of the membrane resonance structure 30a on which the membrane 34 is arranged is parallel to the axis perpendicular to the air outlet 16a of the axial fan 12a. are placed.
When the acoustic resonance structure is a Helmholtz resonance structure or an air column resonance structure, the air in the through holes of the resonance structure is the vibrating body, and the surface in which the through holes are formed is the plane having the vibrating body.

The fan wind is an unsteady fluid phenomenon, and when the unsteady wind collides with the membrane of the membrane-type resonance structure and shakes the membrane, the membrane is vibrated by the wind. The vibration generated in the membrane includes a wide frequency spectrum, and the resonance vibration phenomenon occurs on the membrane surface at the frequency designed as the resonance of the membrane-type resonance structure. In this resonance vibration, the vibration generated in the membrane tends to remain for a long time, and the resonance vibration tends to be amplified while the wind of the fan continues to flow. As a result, sound may be emitted like a speaker from the membrane that is vibrating in resonance. In particular, under conditions where the fan generates a large amount of air, if the resonance structure is arranged so that the air from the fan collides with the membrane surface of the membrane-type resonance structure, the sound will be amplified near the resonance frequency of the membrane-type resonance structure. In some cases, the silencing effect cannot be obtained because the
Therefore, by arranging the surface having the vibrator of the acoustic resonance structure parallel to the axis perpendicular to the blower port of the fan, the airflow generated by the fan can be directed to the surface having the vibrator of the acoustic resonance structure. It is possible to suppress the shaking of the membrane due to collision, and suppress the reduction of the silencing effect due to the wind.

Here, in the example shown in FIG. 1, the fan muffling system is configured to have one membrane-type resonance structure 30a (acoustic resonance structure), but is not limited to this, and is configured to have two or more acoustic resonance structures. may be
For example, as in the example shown in FIG. 4, two membrane-type resonance structures 30a may be arranged at positions downstream of the axial flow fan 12a in the direction of airflow, where the airflow (airflow port 16a) is not blocked. .
In FIG. 4, the two membrane-type resonance structures 30a have the membranes 34 parallel to the rotation axis direction of the axial flow fan 12a, the membranes 34 facing the rotation axis side, and the membranes 34 of the two membrane-type resonance structures 30a. They are arranged so that the side faces face each other.

In addition, in the example shown in FIG. 4, the two membrane-type resonance structures 30a are configured to face each other, but this is not a limitation, and in the example shown in FIG. The membrane-type resonance structures 30a are arranged in the same direction with the membrane surfaces flush with each other, such as the membrane-type resonance structure 30a, the upper two membrane-type resonance structures 30a, and the two left-side membrane-type resonance structures 30a. may be made. Note that FIG. 5 is a view of the fan noise reduction system viewed from the direction of the rotation axis of the axial fan 12a, and the illustration of the axial fan 12a is omitted.

When the fan is connected to the air passage, the membrane resonance structure 30a (acoustic resonance structure) is connected to the wall surface (pipe It may form part of the path 26). Thereby, the membrane-type resonance structure 30a can be arranged at a position that does not block the airflow (airflow port 16a).

In addition, in the example shown in FIG. 1 and the like, the membrane-type resonance structure 30a (acoustic resonance structure) is arranged at a position directly in contact with the axial flow fan 12a (fan). It may be arranged at a position separated from the fan as long as it is arranged within the area.

For example, in the example shown in FIG. 6, the membrane resonance structure 30b is arranged at a position spaced apart from the axial fan 12a, and the conduit 26 is arranged between the membrane resonance structure 30b and the axial fan 12a. It is That is, in the example shown in FIG. 6, a pipe 26 forming a passage of air generated by the axial fan 12a is connected to the downstream side of the axial fan 12a. A membrane-type resonant structure 30b is arranged.

From the viewpoint of arranging the acoustic resonance structure in the near-field region of the sound generated by the fan, the acoustic resonance structure is preferably arranged in contact with the fan or along the outer periphery of the fan casing. When the acoustic resonance structure is a membrane-type resonance structure, it is preferable that the frame of the membrane-type resonance structure is in contact with the casing of the fan. The acoustic resonance structure and the fan may be fixed directly with a screw or the like, fixed via a washer, or fixed via an adhesive or adhesive.

Alternatively, the acoustic resonance structure is preferably placed in contact with the fan via a vibration isolation member.
In the example shown in FIG. 7, the side surface of the frame 32 of the membrane resonance structure 30a is in contact with the axial fan 12a via the vibration isolating member 36. In the example shown in FIG. The membrane resonance structure 30a is in contact with the axial fan 12a via the vibration isolating member 36, thereby suppressing transmission of the vibration of the axial fan 12a to the membrane resonance structure 30a. It is possible to prevent the membranes of the membrane resonance structure 30a from vibrating due to the vibration of the flow fan 12a to generate sound, and to prevent the axial fan 12a and the membrane resonance structure 30a from resonating together.

As the vibration isolating member 36, a member generally used as a vibration isolating member, such as rubber, sponge, or foam, can be used. Further, by using the vibration-isolating member also as a sound-absorbing material, for example, a porous sound-absorbing material, it is possible to obtain both a broadband sound-absorbing effect at high frequencies and suppression of transmission of vibrations to the resonance structure. Specifically, a foamed sound absorber such as Calmflex F2 manufactured by INOAC can be used.

Also, when the fan muffling system has a plurality of acoustic resonance structures, it is preferable to have acoustic resonance structures with different resonance frequencies. Since the fan noise reduction system has an acoustic resonance structure with different resonance frequencies, a higher noise reduction effect can be obtained for a plurality of discrete frequency sounds.
For example, in the example shown in FIG. 8, the fan muffling system has a membrane-type resonance structure 30a and a membrane-type resonance structure 30b. The resonance frequency of the membrane-type resonance structure 30a and the resonance frequency of the membrane-type resonance structure 30b are different.

Here, when the fan muffling system has acoustic resonance structures with different resonance frequencies, the acoustic resonance structure with a higher resonance frequency is arranged closer to the fan than the acoustic resonance structure with a lower resonance frequency. preferable.
In the example shown in FIG. 8, the resonance frequency of the membrane resonance structure 30a arranged closer to the axial fan 12a is higher than the resonance frequency of the membrane resonance structure 30b arranged farther from the axial fan 12a. . As a result, a plurality of discrete frequency sounds can be largely muted.

In the example shown in FIG. 1, etc., the acoustic resonance structure is arranged only on the downstream side of the fan in the air blowing direction of the fan. Alternatively, as in the example shown in FIG. 9, the acoustic resonance structures may be arranged upstream and downstream of the fan. In most equipment, including server fans, it is desirable to be able to place an acoustically resonant structure in the space between the fan and equipment case to reduce noise heard by humans.
From the viewpoint of obtaining a higher silencing effect, the acoustic resonance structure is preferably arranged at least downstream of the fan, and more preferably arranged upstream and downstream of the fan.
When the acoustic resonance structures are arranged upstream and downstream of the fan, the resonance frequency of the upstream acoustic resonance structure and the resonance frequency of the downstream acoustic resonance structure may be the same or different.

Further, the acoustic resonance structure may be configured to have a sound-transmitting windbreak member on the surface side provided with the vibrating body.
Specifically, in the example shown in FIG. 10, the fan muffling system has a membrane-type resonance structure 30a as the acoustic resonance structure, and the surface of the membrane 34, which is the vibrating body of the membrane-type resonance structure 30a, is covered with the membrane 34. It has a windbreak member 48 that is positioned at the bottom.
The windbreak member 48 is a member that allows sound to pass through and prevents wind from entering. By arranging the windbreak member 48 on the surface of the membrane 34, the air current generated by the fan exerts wind pressure on the membrane, which is the vibrating body of the membrane type resonance structure, and suppresses the shaking of the membrane, so that the wind has a silencing effect. reduction can be suppressed.

As the windbreak member 48, a porous structure such as a foam such as a sponge, particularly an open-cell foam, a cloth, a fiber such as a non-woven fabric, or the like can be used. In addition, a rubber material film such as a silicone rubber film with an extremely small Young's modulus, a thin plastic film with a thickness of about 10 μm such as a wrap film, and the like are characterized in that these film materials are loosened and fixed without being tight. can be used. Since these are extremely different in thickness, hardness, and fixing method from the membrane 34 of the membrane-type resonance structure, sound passes through without strong resonance in the audible range.

In addition, in the examples shown in FIGS. 1 to 3, the fan muffling system is configured to have only the membrane-type resonance structure 30a, but is not limited to this, and the fan muffling system may further include a porous sound absorbing material. good too.
For example, a porous sound absorbing material may be provided in the space surrounded by the frame 32 and the film 34 of the membrane-type resonance structure 30a, that is, in the back space 35 . Alternatively, a configuration having a porous sound absorbing material on the surface of the membrane 34 of the membrane resonance structure 30a may be employed.
By configuring the fan muffling system with a porous sound absorbing material, it is possible to muffle sounds of frequencies other than the dominant sound selectively muffled by the resonator in a wide band. Moreover, you may use a porous sound-absorbing material as a windbreak member.

The porous sound absorbing material is not particularly limited, and known porous sound absorbing materials can be appropriately used. For example, urethane foam, soft urethane foam, wood, sintered ceramic particles, phenolic foam, and other foam materials and materials containing microscopic air; glass wool, rock wool, microfiber (thinsulate manufactured by 3M, etc.), floor mats, carpets , meltblown nonwoven fabrics, metal nonwoven fabrics, polyester nonwoven fabrics, metal wool, felt, insulation boards, glass nonwoven fabrics and other fiber and nonwoven fabric materials, wood wool cement boards, nanofiber materials such as silica nanofibers, gypsum boards, etc. of porous sound absorbing materials are available.

The flow resistance of the porous sound absorbing material is not particularly limited, but is preferably 1,000 to 100,000 (Pa·s/m), more preferably 3,000 to 80,000 (Pa·s/m), and more preferably 5,000 to 50,000 (Pa·s/m). s/m2) is more preferred.
The flow resistance of the porous sound absorbing material was obtained by measuring the normal incident sound absorption coefficient of a 1 cm thick porous sound absorbing material and using the Miki model (J. Acoust. Soc. Jpn., 11 (1) pp. 19-24 (1990)). can be evaluated by fitting with Or you may evaluate according to "ISO 9053".
Also, a plurality of porous sound absorbing materials having different flow resistances may be laminated.

Here, in the examples shown in FIGS. 1 to 3, the fan noise reduction system is configured to have the membrane-type resonance structure 30a as the acoustic resonance structure, but is not limited to this. The fan muffling system may have a Helmholtz resonance structure and/or an air column resonance structure as the acoustic resonance structure.

FIG. 11 shows a schematic cross-sectional view of an example of a fan noise reduction system having a Helmholtz resonance structure 40. As shown in FIG. The fan silencer system shown in FIG. 11 has the same configuration as the fan silencer system shown in FIG. 4 except that it has a Helmholtz resonance structure 40 instead of the membrane resonance structure 30a as the acoustic resonance structure.

In the example shown in FIG. 11 the acoustic resonance structure is a Helmholtz resonance structure 40 . The Helmholtz resonance structure 40 includes a prismatic frame 42 having an opening with a bottom surface on one side, and a peripheral edge portion that covers the opening of the frame 32 and is fixed to the frame 32 . and a plate-like lid portion 44 having a through hole 46 . In the Helmholtz resonance structure 40, the air in the internal space 43 surrounded by the frame 42 and the lid 44 acts as a spring, and the air in the through hole 46 formed in the lid 44 acts as a mass. , the mass spring resonates, and the thermal-viscous friction in the vicinity of the wall of the through-hole 46 absorbs sound.

In the example shown in FIG. 11, the lid portion 44 having the through hole 46 is arranged parallel to the rotation axis direction of the axial fan 12a, and the lid portion 44 faces the rotation axis side.

Conventionally, when a Helmholtz resonance structure is used for silencing, the resonance frequency of the Helmholtz resonance structure is adjusted to the frequency of the sound to be muted, thereby muting the sound at that frequency. Therefore, there is a problem that the effect of silencing is low for sounds in frequency bands other than the resonance frequency, and it is difficult to silencing a plurality of discrete frequency sounds generated by the fan.

On the other hand, in the fan noise reduction system of the present invention, the Helmholtz resonance structure 40 is arranged in the near-field region of the sound generated by the fan, thereby generating the two interaction mechanisms described above, and the fan generates Multiple discrete frequency sounds can be silenced.

Even when the Helmholtz resonance structure 40 is used as the acoustic resonance structure, it is preferable that the resonance frequency of the Helmholtz resonance matches any one frequency of the discrete frequency sounds generated by the axial flow fan 12a.
The resonance frequency of the Helmholtz resonance is determined by the volume of the internal space surrounded by the frame 42 and the lid 44 and the area, length, etc. of the through-hole 46 . Therefore, by adjusting the volume of the internal space surrounded by the frame 42 and the lid 44 of the Helmholtz resonance structure 40 and the area, length, etc. of the through hole 46, the resonance frequency can be appropriately set.

Here, in the example shown in FIG. 11 , the through hole 46 is formed in the lid portion 44 , but the configuration is not limited to this, and the through hole 46 may be formed in the frame 42 . However, at this time, the inlet/outlet of the through-hole must face the direction in which the discrete frequency sound generated by the axial fan 12a propagates, which is the flow direction of the fan in FIG.
In the example shown in FIG. 11, the Helmholtz resonance structure 40 has the frame body 42 and the lid part 44 which are separate bodies, but the frame body 42 and the lid part 44 may be integrally formed.

In the Helmholtz resonance structure 40, the air in the through-hole 46 is the vibrating body, and the surface of the lid portion 44 having the through-hole 46 is the surface on which the vibrating body is provided. Therefore, it is preferable that the surface of the lid portion 44 having the through hole 46 is arranged parallel to the axis perpendicular to the blower port. Also, a windbreak member may be arranged on the surface of the lid portion 44 .

Further, the shape of the Helmholtz resonance structure 40 viewed from the direction perpendicular to the surface of the lid portion 44 may be square, polygonal such as triangular, circular, elliptical, or the like.

In the example shown in FIG. 11, the fan silencer system has two Helmholtz resonance structures 40, but is not limited to this, and may have one Helmholtz resonance structure, or three or more Helmholtz resonance structures. It is good also as a structure which has. In the case of a configuration having a plurality of Helmholtz resonance structures, the frame of each Helmholtz resonance structure may be integrally formed, or the internal space may be shared.
Moreover, in the case of a configuration having a plurality of Helmholtz resonance structures, a configuration having Helmholtz resonance structures with different resonance frequencies may be used.

Further, in the present invention, the resonator of the muffler may have an air column resonance structure.
In the air column resonance structure, resonance occurs when a standing wave is generated in a resonance tube having an opening.

Conventionally, when an air column resonance structure is used for silencing, the resonance frequency of the air column resonance structure is adjusted to the frequency of the sound to be muted, thereby muting the sound of that frequency. Therefore, there is a problem that the effect of silencing is low for sounds in frequency bands other than the resonance frequency, and it is difficult to silencing a plurality of discrete frequency sounds generated by the fan.

On the other hand, in the fan noise reduction system of the present invention, by placing the air column resonance structure in the near-field region of the sound generated by the fan, the two interaction mechanisms described above are generated, and the fan generates Multiple discrete frequency sounds can be silenced.

Even when an air column resonance structure is used as the acoustic resonance structure, it is preferable that the resonance frequency of the air column resonance matches any one of discrete frequency sounds generated by the fan.
The resonance frequency of air column resonance is determined by the length of the resonance tube and the like. Therefore, by adjusting the depth of the resonance tube, the size of the opening, etc., it is possible to appropriately set the frequency of the sound that resonates.

When the acoustic resonance structure has an internal space and a through hole (opening) that communicates the internal space with the outside, the resonance structure causes air column resonance or the resonance structure causes Helmholtz resonance. It is determined by the size and position of the through hole, the size of the internal space, and the like. Therefore, by appropriately adjusting these, it is possible to select either the air column resonance or the Helmholtz resonance structure.
In the case of the air column resonance structure, if the opening is narrow, the sound wave will be reflected by the opening, making it difficult for the sound wave to enter the internal space. Specifically, when the opening is rectangular, the length of the short side is preferably 1 mm or more, more preferably 3 mm or more, and even more preferably 5 mm or more. When the opening is circular, the diameter is preferably within the above range.
On the other hand, in the case of Helmholtz resonance, since it is necessary to generate thermoviscous friction in the through-hole, it is preferable that the through-hole be narrow to some extent. Specifically, when the through hole has a rectangular shape, the length of the short side is preferably 0.5 mm or more and 20 mm or less, more preferably 1 mm or more and 15 mm or less, and even more preferably 2 mm or more and 10 mm or less. When the through hole is circular, the diameter is preferably within the above range.

Note that the fan noise reduction system of the present invention may be configured to have different types of acoustic resonance structures. For example, a configuration having a Helmholtz resonance structure and a membrane-type resonance structure may be used.
Here, it is preferable to use a film-type resonance structure as the acoustic resonance structure from the viewpoint of miniaturization and thinning.

Materials for the frame and lid of the membrane resonance structure, Helmholtz resonance structure, and air column resonance structure (hereinafter collectively referred to as "frame materials") include metal materials, resin materials, reinforced plastic materials, carbon fibers, and the like. can be mentioned. Examples of metal materials include metal materials such as aluminum, titanium, magnesium, tungsten, iron, steel, chromium, chromium molybdenum, nichrome molybdenum, copper, and alloys thereof. Examples of resin materials include acrylic resin, polymethyl methacrylate, polycarbonate, polyamideimide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, Resin materials such as ABS resin (acrylonitrile, butadiene, styrene copolymer synthetic resin), polypropylene, and triacetyl cellulose can be mentioned. Examples of reinforced plastic materials include carbon fiber reinforced plastics (CFRP) and glass fiber reinforced plastics (GFRP). Also included are natural rubber, chloroprene rubber, butyl rubber, EPDM (ethylene-propylene-diene rubber), silicone rubber, and rubbers containing these crosslinked structures.
Various honeycomb core materials can also be used as the frame material. Since the honeycomb core material is lightweight and used as a high-rigidity material, ready-made products are readily available. Aluminum honeycomb core, FRP honeycomb core, paper honeycomb core (manufactured by Shinnihon Feather Core Co., Ltd., Showa Aircraft Industry Co., Ltd., etc.), thermoplastic resin (PP, PET, PE, PC, etc.) honeycomb core (manufactured by Gifu Plastic Industry Co., Ltd.) A honeycomb core material formed of various materials such as TECCELL, etc.) can be used as the frame.
A structure containing air, that is, a foam material, a hollow material, a porous material, or the like can also be used as the frame material. In the case of using a large number of resonators, the frame can be formed using, for example, closed-cell foam material in order to prevent ventilation between the cells. For example, a variety of materials can be selected such as closed-cell polyurethane, closed-cell polystyrene, closed-cell polypropylene, closed-cell polyethylene, and closed-cell rubber sponge. By using a closed-cell body, it is suitable for use as a frame material because it is impervious to sound, water, gas, etc. and has a high structural strength compared to an open-cell body. In addition, when the porous sound absorbing body described above has sufficient supportability, the frame may be formed of only the porous sound absorbing body, and the porous sound absorbing body and the material of the frame may be mixed, for example. , may be used in combination by kneading or the like. In this way, the weight of the device can be reduced by using a material system containing air inside. In addition, heat insulation can be imparted.

Here, the frame material is preferably made of a material having higher heat resistance than the flame-retardant material, because it can be placed in a high-temperature position. Heat resistance can be defined, for example, by the time that satisfies each item of Article 108-2 of the Enforcement Ordinance of the Building Standards Law. If the time satisfying each item of Article 108-2 of the Building Standards Law Enforcement Ordinance is 5 minutes or more and less than 10 minutes, it is a flame-retardant material. The above cases are noncombustible materials. However, heat resistance is often defined for each field. Therefore, in accordance with the field in which the fan noise reduction system is used, the frame material may be made of a material having heat resistance equivalent to or higher than the flame retardancy defined in the field.

The thickness of the frame and lid (frame thickness) is also not particularly limited, and can be set according to, for example, the size of the cross section of the opening of the frame.

Materials for the film 34 include aluminum, titanium, nickel, permalloy, 42 alloy, kovar, nichrome, copper, beryllium, phosphor bronze, brass, nickel silver, tin, zinc, iron, tantalum, niobium, molybdenum, zirconium, gold, Various metals such as silver, platinum, palladium, steel, tungsten, lead, and iridium; PET (polyethylene terephthalate), TAC (triacetylcellulose), PVDC (polyvinylidene chloride), PE (polyethylene), PVC (polyvinyl chloride ), PMP (polymethylpentene), COP (cycloolefin polymer), Zeonor, polycarbonate, PEN (polyethylene naphthalate), PP (polypropylene), PS (polystyrene), PAR (polyarylate), aramid, PPS (polyphenylene sulfide) , PES (polyethersulfone), nylon, PEs (polyester), COC (cyclic olefin copolymer), diacetylcellulose, nitrocellulose, cellulose derivatives, polyamide, polyamideimide, POM (polyoxymethylene), PEI (polyetherimide) ), polyrotaxane (slide ring material, etc.), and resin materials such as polyimide. Furthermore, glass materials such as thin film glass, and fiber-reinforced plastic materials such as CFRP (carbon fiber reinforced plastic) and GFRP (glass fiber reinforced plastic) can also be used. In addition, natural rubber, chloroprene rubber, butyl rubber, EPDM, silicone rubber, etc. and rubbers containing these crosslinked structures can be used. Alternatively, a combination thereof may be used.
Moreover, when a metal material is used, the surface may be plated with a metal from the viewpoint of suppressing rust.

From the viewpoint of excellent durability against heat, ultraviolet rays, external vibration, etc., it is preferable to use a metal material as the material of the film 34 in applications where durability is required.

The method of fixing the film or lid to the frame is not particularly limited, and a method using double-sided tape or an adhesive, a mechanical fixing method such as screwing, crimping, or the like can be used as appropriate. The fixing method can also be selected from the viewpoint of heat resistance, durability, and water resistance in the same manner as the frame material and membrane. For example, the adhesive can be selected from Cemedine "Super X" series, ThreeBond "3700 series (heat resistant)", and heat-resistant epoxy adhesive "Duralco series" manufactured by Taiyo Wire Net Co., Ltd. As the double-sided tape, 3M's highly heat-resistant double-sided adhesive tape 9077 or the like can be selected. In this way, various fixation methods can be selected for the required properties.

Here, in the example shown in FIG. 1 and the like, the fan silencing system has an axial fan 12a as a fan, and is configured to suppress the noise of the axial fan (propeller fan), but it is not limited to this, and Sirocco It can be applied to conventionally known fans such as fans, turbo fans, centrifugal fans, and line flow fans.
A sirocco fan takes in air from the direction of the rotation axis of a rotor having blades and sends air in a direction perpendicular to the rotation axis, and has an air outlet on the side surface. Therefore, for example, as shown in FIG. 12, when the fan is a sirocco fan 12b, the membrane-type resonance structure 30a (acoustic resonance structure) is arranged so as to be in contact with the blower port . The configuration of the membrane-type resonance structure 30a is the same as the example shown in FIG.

In the example shown in FIG. 12, the membrane-type resonance structure 30a is arranged at a position that does not block the air outlet of the sirocco fan 12b. Further, the membrane-type resonance structure 30a is arranged such that the membrane 34 is parallel to the direction perpendicular to the blower port of the sirocco fan 12b and the membrane 34 faces the blower port side.

In this way, even in the case of the sirocco fan, since sound is generated from the blades of the fan, the near-field region is a region at a distance of less than λ/4 from the blades of the fan. Therefore, by arranging the acoustic resonance structure within the near-field region, it is possible to generate the above-described two interactions within the near-field region and obtain a silencing effect.

The present invention will be described in more detail below based on examples. The materials, amounts used, proportions, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the examples shown below.

[Comparative Example 1]
An axial flow fan (Model: 109P0612K701 manufactured by Sanyo Denki Co., Ltd.) was used as the fan. This axial fan has an outer diameter of 60 mm×60 mm and a thickness of 15 mm. Since the casing is attached to the exhaust side of the fan, the distance from the front end of the blower port to the blades of the rotor is about 5 mm.
In order to suppress the influence of solid vibration from the fan, a 5 mm thick anti-vibration rubber was placed under the fan. In addition, in order to suppress the sound emitted from the side of the fan as solid vibration, the side of the fan casing was surrounded by acrylic with a thickness of 5 mm.

A square duct with an inner diameter of 60 mm square equal to the outer diameter of the fan and a length in the duct direction of 30 mm was produced by cutting and combining rectangular plates with a short side length of 30 mm using an acrylic plate with a thickness of 5 mm. . The acrylic plate was processed using a laser cutter.
This duct was placed on the surface of the fan on the air outlet side, matching the cross section of the fan's air passage and the duct. By connecting the frame surrounding the casing of the fan and the outside of the duct with tape to completely close it, a structure in which the duct is in close contact with the fan as shown in FIG. 13 was produced.

<Measurement>
Using the fabricated structure, the fan was driven and the sound volume was measured.
The sound was measured at a position 200 mm away from the center of the fan in the axial direction, and a microphone (Accor 1/2 inch microphone 4152) was placed at a point offset by 50 mm from the center axis in both horizontal and vertical directions to avoid the effect of wind. placed. Microphones were placed on both the exhaust and supply sides.
The fan was driven using a DC stabilized power supply. The driving conditions of the fan were set to 12V and 0.25A.

FIG. 14 shows the results of measurement with the exhaust-side microphone. The horizontal axis of the graph shown in FIG. 14 is represented logarithmically. From FIG. 14, it can be seen that a large peak sound (narrow band sound), which is characteristic of a fan with rotating blades, appears at multiple frequencies. That is, it can be seen that a discrete frequency sound is generated. Among them, a large peak has a relationship of integral multiples. In particular, the volume of 1.1 kHz and 2.2 kHz is large.

Further, when the wind speed at the end of the duct on the exit side was measured using an anemometer, it was 3.1 m/s. No change was observed in the wind speed up to Example 3.

[Example 1]
A fan noise reduction system was produced in the same manner as in Comparative Example 1, except that the inner wall of the duct was made to have a membrane-type resonance structure produced as follows. The resonance frequency of the membrane-type resonance structure was set to 2.2 kHz.

<Design of membrane-type resonance structure>
Acoustic-structure interaction calculation by the finite element method was performed using COMSOL MULTIPHYSICS (manufactured by COMSOL Inc.) to design a membrane-type resonance structure. The material of the membrane was PET, the thickness was 75 μm, and the design was performed by changing the size and the back distance. It was found that a membrane-type resonance structure having a circular frame with an inner diameter of 24 mm and a back surface distance of 6 mm, which is the vibrating portion of the membrane, has resonance at 2.2 kHz and high absorption.
The back surface distance of 6 mm corresponds to a distance of 0.038×λ with respect to the wavelength λ of 2.2 kHz, and it can be seen that resonance can be achieved with a very thin structure. Since the required length is 0.25×λ in the case of a normal one-side closed air column resonance structure, it can be seen that the thickness can be reduced to about 15% of the size of the air column resonance structure.

<Fabrication of membrane-type resonance structure>
The structure designed above was produced by processing an acrylic plate with a laser cutter. Specifically, by processing an acrylic plate with a thickness of 3 mm, two perforated plate members having a square shape with an outer shape of 30 mm and an opening with a diameter of 24 mm in the perforated plate member, and a square plate member with an outer shape of 30 mm. made. Two perforated plate members and a plate member were superimposed in this order and adhered with a double-faced tape (Chikara of ASKUL Co., Ltd.) to produce a frame.

A PET film (Lumirror manufactured by Toray Industries, Inc.) having a thickness of 75 μm was adhered to the opening surface of the frame with a double-sided tape. By cutting the PET film according to the outer shape of the frame, a film-type resonance structure having an outer shape of 30 mm square, an inner diameter of the frame of 24 mm, a thickness of the PET film of 75 μm, and a back-to-back distance of 6 mm was produced.
Six such membrane-type resonance structures were produced, and a duct (30 mm in length) having two membrane-type resonance structures on each of three of the four surfaces of the duct was produced (see FIG. 5).

<Measurement>
The fan of the manufactured fan muffling system was driven, and the sound volume was measured on the exhaust side and the intake side in the same manner as in Comparative Example 1.
FIG. 15 shows the measurement results on the exhaust side, and FIG. 16 shows the measurement results on the intake side. 15 and 16 also show the results of Comparative Example 1. FIG.

From FIG. 15, it can be seen that a large silencing effect of about 20 dB can be obtained at the resonance frequency of 2.2 kHz of the membrane type resonance structure. Furthermore, it can be seen that the noise reduction effect can also be obtained for a plurality of discrete frequency sounds with different frequencies generated by the rotation of the fan, as indicated by the arrows in FIG. That is, it can be seen that the silencing effect can be obtained even at frequencies other than the resonance frequency of the membrane-type resonance structure. In this way, the fan noise reduction system of the present invention can silence the sound of frequencies other than the resonance frequency of the acoustic resonance structure by arranging the acoustic resonance structure in the near-field region of the sound generated by the fan. It can be seen that a plurality of discrete frequency sounds with different frequencies generated by are muted.
Further, by matching the resonance frequency of the membrane-type resonance structure to one frequency among a plurality of discrete frequency sounds with different frequencies generated by the fan rotation, it is possible to further enhance the silencing effect at that frequency. Recognize.

Also, from FIG. 16, it can be seen that the sound volume is reduced at the resonance frequency of the membrane-type resonance structure and other frequencies on the intake side as well. That is, it can be seen that the silencing effect on the exhaust side is not that the sound is reflected and output to the intake side, but that the noise is muted on both the exhaust side and the intake side. This effect is thought to be due to the absorption of sound by membrane vibration by the membrane-type resonance structure, the sound reflected by the membrane-type resonance structure, and the interference with the sound source, thereby suppressing the phenomenon of sound emitted from the sound source.

In the fan noise reduction system of Example 1, the distance between the sound source portion (blade) of the fan and the center of the membrane vibrating portion of the membrane resonance structure is "5 mm distance from the front surface of the fan blade to the front surface of the blowing port" + "membrane resonance The distance from the center position of the membrane of the structure to the front face of the fan's air outlet is 15 mm'=20 mm. Since the wavelength/4 of the frequency of 2.2 kHz is 39 mm, it can be seen that the film-type resonance structure is arranged within the near-field region.

[Comparative Example 2]
In Comparative Example 2, as shown in FIG. 17, the membrane resonance structure 30a is arranged apart from the axial fan 12a, and the duct 100 is arranged between the membrane resonance structure 30a and the axial fan 12a. . The membrane-type resonance structure 30a used was the same as the membrane-type resonance structure of the first embodiment. The duct 100 was similar to the duct of Comparative Example 1 except that the length was 60 mm.
In this configuration, the distance between the sound source portion (blades) of the fan and the membrane-type resonance structure is 80 mm. Therefore, the membrane-type resonance structure 30a is arranged outside the near-field region.

<Measurement>
The fan of the fan silencer system of Comparative Example 2 was driven, and the sound volume was measured on the exhaust side and the intake side in the same manner as in Comparative Example 1. In Comparative Example 2, the sound volume measurement results were compared with those obtained when the membrane-type resonance structure 30a was replaced with a duct, and the silencing volume was obtained from the difference.
The results are shown in FIG.
FIG. 19 shows the sound volume measurement results of Comparative Example 3 and the case where the portion of the membrane-type resonance structure 30a of Comparative Example 3 is replaced with a duct (simple duct).

From FIG. 18, it can be seen that in Comparative Example 2, noise can be silenced at the resonance frequency of the membrane-type resonance structure 30a.
However, from FIG. 19 showing a wider frequency range, it can be seen that in the structure of Comparative Example 3, the silencing effect cannot be obtained at frequencies other than the resonance frequency of the membrane-type resonance structure 30a.
In Comparative Example 2, since the membrane-type resonance structure and the sound source are separated from each other by λ/2, the interference effect (far-field interference) of normal sound waves produces a silencing effect. On the other hand, it is considered that the mechanism in the above-mentioned near-field region does not occur, so it is natural that it does not contribute to silencing other than the resonance frequency of the membrane-type resonance structure.

On the other hand, when the membrane-type resonance structure is placed in the near-field region as in Example 1, the interaction between the membrane-type resonance structure and the sound source is treated as an integrated unit, and furthermore, a high wave number that does not propagate far It is also necessary to consider the interaction of the near-field sound of In this case, it is considered that the above-described mechanism contributed to the amount of sound emitted at frequencies other than the resonance frequency of the membrane-type resonance structure. Therefore, in the near-field region, a silencing effect can be provided for sounds in a wide frequency band.

From the above results, it can be seen that a plurality of discrete frequency sounds generated by the fan can be silenced by arranging the film-type resonance structure in the near-field region as in Example 1 of the present invention. It is also found that by matching the resonance frequency of the membrane-type resonance structure with one frequency of the discrete frequency sound, a higher noise reduction effect can be obtained at this frequency. Also, it can be seen that the fan noise can be silenced without blocking the air passage.

[Example 2]
Using the same film-type resonance structure as in Example 2, a study was conducted in which the type of fan was changed to change the peak sound frequency. A Sanyo Denki DC axial flow fan "9GA0612G9001" (frame size 60 mm, thickness 10 mm) was used. When this fan is fixed in the same manner as in Example 1, and the same membrane type resonance structure as in Example 1 is attached to the exhaust side (Example 2), there is no resonance structure at the same position, but the length of the duct is the same. Each measurement was performed when a duct with a height of 30 mm was attached (Comparative Example 3).

FIG. 20 shows the measurement results. In the case of this fan, the peak sound frequency appears at a frequency shifted from the resonance frequency of the membrane-type resonance structure. Around 2.2 kHz, which is the resonance frequency of the membrane-type resonance structure, a relatively wide silencing of about 8 dB appears. On the other hand, at the fan peak sound frequencies (1.2 kHz, 2.4 kHz, and 3.6 kHz), when the film-type resonance structure is in the near-field region, the original peak sound volume can be reduced.
As described above, it can be seen that the resonance structure in the near-field region can muffle the peak sound frequency of the fan that deviates from the resonance frequency of the membrane-type resonance structure.
Regarding the amount of peak noise reduction, the case of the first embodiment in which the resonance frequency is matched with the fan peak sound frequency is higher than the case of the present embodiment in which the resonance frequency is shifted from the fan peak sound frequency. It can be seen that the silencing volume is large and preferable.

[Example 3]
A membrane-type resonance structure was fabricated in the same manner as in Example 1, except that the resonance frequency of the membrane-type resonance structure was 1.1 kHz.

<Fabrication of membrane-type resonance structure>
Designing by the finite element method using COMSOL MULTIPHYSICS revealed that the resonance frequency was 1.1 kHz by changing the back surface distance of the membrane-type resonance structure of Example 1 from 6 mm to 15 mm. This film-type resonance structure was fabricated in the same manner as in Example 1 by processing an acrylic plate with a laser cutter.

The manufactured membrane-type resonance structure was arranged at a position separated by 30 mm from the surface of the blower port of the fan. A duct was connected between the membrane resonance structure and the fan (see FIG. 6). The distance from the center of the membrane-type resonance structure to the fan sound source portion (blade) is 50 mm. On the other hand, since the wavelength/4 of the frequency of 1.1 kHz is 78 mm, it can be seen that the film-type resonance structure is arranged within the near-field region.

<Measurement>
The fan of the manufactured fan silencer system was driven and the sound volume was measured on the exhaust side and the intake side in the same manner as in Example 1.
The results are shown in FIG. FIG. 21 also shows the sound volume measurement results when the membrane-type resonance structure of Example 3 is replaced with a duct (simple duct).

From FIG. 21, it can be seen that a large noise reduction effect of about 10 dB can be obtained at the resonance frequency of 1.1 kHz of the membrane type resonance structure. Furthermore, it can be seen that the silencing effect can be obtained even with respect to a plurality of discrete frequency sounds generated by the fan.

[Example 4]
A fan muffling system in the same manner as in Example 1 except that the membrane-type resonance structure produced in Example 3 is arranged downstream of the membrane-type resonance structure of the fan muffling system of Example 1 (see FIG. 8). was made.
The results are shown in FIG. FIG. 22 also shows the sound volume measurement results when the membrane-type resonance structure of Example 4 is replaced with a duct (simple duct).

It can be seen that a large silencing effect of about 15 dB can be obtained at resonance frequencies of 1.1 kHz and 2.2 kHz for each of the membrane-type resonance structures. In other words, it can be seen that even if the membrane-type resonance structures are arranged in series, each of the silencing effects functions.
Moreover, it can be seen that the noise reduction effect can be obtained for a plurality of discrete frequency sounds generated by the fan as indicated by the arrows in FIG. That is, it can be seen that the silencing effect can be obtained even at frequencies other than the resonance frequency of the membrane-type resonance structure.

The difference between the two data in FIG. 22 is taken and shown in FIG. 23 as the muting volume. In the vicinity of 1.1 kHz and in the vicinity of 2.2 kHz, the noise peak of the fan is reduced by 15 dB or more, and the noise reduction effect is also obtained in other frequency bands.

To evaluate the perceived loudness of the fan silencer system of Example 4, an octave band rating and an overall noise volume rating were presented. FIG. 24 shows the result of evaluation for each 1/3 octave band and the A characteristic evaluation (unit: dBA) that is correction considering the sensitivity of the human ear. By eliminating the noise peaks at 1.1 kHz, 2.2 kHz, and other frequencies, it can be seen that the overall sound is reduced even in the 1/3 octave band evaluation, which evaluates by averaging the frequencies widely. . In addition, A-characteristic correction was performed for the entire audible frequency band and integrated to calculate the noise level. The noise level, which was 81.9 (dBA) in the simple duct, was reduced to 74.9 (dBA) in the fan silencer system of Example 4. When the noise level has a difference of 3 dBA, it is said that ordinary people can sufficiently detect it.
In this way, we conducted a study to suppress the discrete frequency sound generated by the fan, and by placing the acoustic resonance structure in the near-field region, not only the resonance frequency but also the entire discrete frequency sound generated by the fan were silenced. It was shown that a large noise reduction effect can be obtained by

[Example 5]
In order to perform measurements under stronger wind conditions than in Examples 1 to 4, the type of fan was changed. A 9GA0612P1J03 (thickness: 38 mm) fan manufactured by Sanyo Denki was used. FIG. 25 shows the wind speed when the amount of current supplied to this fan is changed. By increasing the amount of current, a high air velocity and high air volume can be obtained.

A film-type resonance structure having the same configuration as that of the second embodiment was arranged on the exhaust side of this fan. However, the film surface of the film-type resonance structure was lowered by 5 mm to the outer peripheral side from that of Example 2 (see FIG. 26). This is for arranging a windbreak member in Example 6 which will be described later.

<Measurement>
The fan of the manufactured fan muffling system was driven, and the sound volume was measured on the exhaust side and the intake side in the same manner as in Comparative Example 1.
FIG. 27 shows the measurement results on the exhaust side. In addition, as Comparative Example 4, measurement results obtained when the membrane-type resonance structure of Example 5 is replaced with a duct are also shown. Example 5 and Comparative Example 4 have the same structural length of 30 mm in the flow direction.
In addition, the wind speed at the outlet side end of Example 4 and Comparative Example 4 was measured using an anemometer. As a result, both were 14.5 m/s, and it was confirmed that the wind speed did not change between the case where the membrane type resonance structure was attached and the case where the cylinder structure was installed.

It can be seen from FIG. 27 that the peaks of frequencies other than the resonance frequency of the membrane-type resonance structure can obtain the noise reduction effect as indicated by the arrows in FIG. However, with respect to the peak around 1.1 kHz, which is the resonance frequency, there is an effect that the sound is amplified in the surrounding frequencies, and it can be seen that the peak silencing effect is hardly obtained.
In Example 5, since the fan has a large air volume and is a rotating fan, the air flow is unsteady. The wind exerts wind pressure on the film surface, causing the film surface to vibrate due to the wind. The vibration generated in the membrane includes a wide frequency spectrum, among which the resonance phenomenon occurs at and around the frequency designed as resonance in the design of the membrane-type resonance structure, that is, the frequency aimed at silencing. At this resonance frequency, the vibration generated on the film surface tends to remain for a long time, and its amplitude tends to be amplified while the fan continues to operate. Therefore, the sound is emitted from there like a speaker. In this way, when a strong air volume is generated in the very vicinity of the fan, the sound is amplified in the vicinity of the resonance frequency, and it is considered that the desired noise reduction effect could hardly be obtained.

[Example 6]
A fan noise reduction system of Example 5 was produced in the same manner as in Example 5, except that a windbreak member was arranged on the surface of the membrane of the membrane type resonance structure (see FIG. 10).
A urethane sponge (thickness: 5 mm) was used as a windbreak member. In order to prevent the influence of the vibration of the membrane as much as possible, do not use double-sided tape or the like on the membrane side of the sponge, but put scotch tape on a part of the air side of the sponge (the position that hits the frame of the membrane-type resonance structure at the bottom of the sponge). was used to attach the sponge to the side wall of the membrane-type resonance structure so that the sponge would not be displaced from the membrane-type resonance structure.

<Measurement>
The fan of the manufactured fan muffling system was driven, and the sound volume was measured on the exhaust side and the intake side in the same manner as in Comparative Example 1.
FIG. 28 shows the measurement results on the exhaust side. The measurement results of Comparative Example 4 are also shown at the same time.
In addition, the wind speed at the outlet side end of Example 6 was measured using an anemometer. As a result, it was 14.5 m/s, and it was confirmed that the wind speed did not change.

From FIG. 28, it can be seen that the amplification of sound near the resonance frequency (1.1 kHz) that occurred in Example 5 can be greatly suppressed. In addition, as indicated by arrows in FIG. 28, it can be seen that the effect of reducing peak sounds of frequencies other than the resonance frequency is also obtained. In addition, it can be seen from FIG. 28 that noise can be eliminated over a wide band in the high frequency range of 5.4 kHz or higher. This is the sound absorbing effect of the sponge placed on the film surface.
From the above results, by placing the windbreak member on the surface of the membrane, it is possible to greatly suppress the phenomenon of sound in the vicinity of the resonance frequency when the membrane-type resonance structure is arranged very close to the fan. I understand. It is also found that the use of the porous sound absorbing material as the windbreak member achieves both the sound damping effect of the porous sound absorbing material and the sound damping effect of the membrane-type resonance structure.

[Example 7]
A fan muffling system was produced in the same manner as in Example 5, except that a Helmholtz resonance structure was used as the acoustic resonance structure.
When a Helmholtz resonance structure with a resonance frequency of 1.1 kHz was designed, the length of the through hole was 3 mm, the diameter of the through hole was 4 mm, the thickness of the internal space was 12 mm, and the diameter of the internal space was 24 mm.
A Helmholtz resonance structure was produced by processing an acrylic plate with a laser cutter so as to have such a configuration. A fan noise reduction system was produced in the same manner as in Example 5 so that the 6-cell Helmholtz resonance structure constituted the duct wall surface.

FIG. 29 shows the measurement results when the amount of current supplied to the fan is 0.3A. Also shown is the measurement result when a duct of the same length was attached instead of the Helmholtz resonance structure (Comparative Example 5). At this time, the wind speed was 5.5 m/s.

From FIG. 29, it can be seen that even when the Helmholtz resonance structure is used as the acoustic resonance structure, a silencing effect can be obtained for peak sounds of frequencies other than the resonance frequency. On the other hand, the 1.1 kHz peak, which is the resonance frequency, is slightly muted, and the sound is amplified around it. This is the effect that, in the wind noise generated in the through-hole portion of the Helmholtz resonance structure, resonance occurs at the resonance frequency of the resonance structure, the sound is amplified, and the sound is produced.

[Example 8]
The sound volume was measured in the same manner as in Example 7 except that the current supplied to the fan was 1.3A. FIG. 30 shows the measurement results. Also shown is the measurement result when a duct of the same length was attached instead of the Helmholtz resonance structure (Comparative Example 6). Also, the wind speed was 15.1 m/s.

From FIG. 30, it can be seen that the effect of silencing a plurality of peak sounds of frequencies other than the resonance frequency can be obtained even with the Helmholtz resonance structure under high air volume. On the other hand, it can be seen that the wind noise amplified by resonance becomes louder as the wind speed increases, and the peak sound near the resonance frequency is amplified.
From the above, it can be seen that the effect that a plurality of discrete frequency sounds can be silenced by the resonance structure is not limited to the membrane type resonator and is general. In addition, the amplification effect of this Helmholtz resonance due to wind noise is greater than the phenomenon of ringing with a membrane-type resonance structure.

[Comparative Example 7]
In order to study the application to fans other than axial fans, we examined the application to sirocco fans for blowers. A blower 9BMC12P2G001 manufactured by Sanyo Denki was used. This blower fan was placed on a vibration isolator with a thickness of 10 mm, and the air taken in from above was discharged horizontally. At a position 30 mm away from the air outlet, an acrylic plate 102 with a thickness of 5 mm having an opening of the same size as the air outlet (an opening of about 30 mm × 52 mm) was placed as a screen 102, and the position was such that the wind did not hit directly on the tip. An experiment was conducted by arranging a measurement microphone MP. The wind speed measured at the opening of the screen 102 at this time was 7.7 m/s.

Measurement was performed in a state in which the air outlet and the opening of the screen 102 were connected by a duct 100 made of an acrylic plate having a thickness of 5 mm. A schematic diagram is shown in FIG.

[Example 9]
A fan muffling system was produced in the same manner as in Comparative Example 7, except that four membrane-type resonance structures 30a of Example 4 were arranged in a duct shape between the air outlet and the opening of the screen 102 (see FIG. 32). .
The minimum distance between the membrane-type resonance structure 30a and the blades of the sirocco fan is 24 mm, and the membrane-type resonance structure 30a is arranged in the near-field region.

<Measurement>
In Example 9 and Comparative Example 7, the fan was driven and the sound volume was measured with the measurement microphone MP.
The measurement results are shown in FIG.

From the results shown in FIG. 33, it can be seen that the configuration of Example 9 can reduce the peak sound in the vicinity of the resonance frequency, and that the peak sound appearing at other frequencies also has a silencing effect. From this result, it is shown that even in the sirocco fan, as in the case of the axial fan, by arranging the acoustic resonance structure in the near-field region, it is possible to obtain the effect of silencing a plurality of discrete frequency sounds.
From the above results, the effect of the present invention is clear.

REFERENCE SIGNS LIST 10 Fan noise reduction system 12a Axial fan 12b Sirocco fan 16 Casing 16a Blower port 18 Rotor 20 Shaft 22 Blades 26 Pipe 30a, 30b Membrane resonance structure 32, 42 Frame 34 Membrane 35 Back space 36 Anti-vibration member 38 Blower Mouth 40 Helmholtz resonance structure 43 Internal space 44 Lid 46 Through hole 48 Windbreak member 100 Duct 102 Screen MP Microphone

Claims (13)

having a fan and an acoustic resonance structure;
wherein the acoustic resonance structure is positioned within a near-field region of sound generated by the fan;
A fan muffling system according to claim 1, wherein a surface of said acoustic resonance structure having a vibrating body is arranged parallel to an axis perpendicular to an air outlet of said fan and parallel to a rotation axis direction of said fan. 2. The fan muffling system of claim 1, wherein a resonant frequency of said acoustic resonance structure matches at least one frequency of discrete frequency sound caused by rotation of said fan blades. 3. The claim 1 or 2, wherein when viewed from a direction perpendicular to the blower opening of the fan, an area where the acoustic resonance structure overlaps with the blower opening is 50% or less of the area of the blower opening. fan silence system. The fan noise reduction system according to any one of claims 1 to 3, wherein the acoustic resonance structure constitutes a part of a wall surface of an air passage connected to the fan. The fan muffling system according to any one of claims 1 to 4, further comprising a sound-transmitting windbreak member on the side of the acoustic resonance structure having the vibrator. The fan muffling system according to any one of claims 1 to 5, wherein the acoustic resonance structure is in contact with the fan. 7. The fan muffling system according to claim 6, wherein said acoustic resonance structure is in contact with said fan through a vibration isolating member. having a plurality of said acoustic resonance structures with different resonance frequencies;
The fan muffling system according to any one of claims 1 to 7, wherein the acoustic resonance structure with a higher resonance frequency is arranged closer to the fan than the acoustic resonance structure with a lower resonance frequency. The fan muffling system according to any one of claims 1 to 8, wherein the acoustic resonance structure is arranged only on the downstream side of the fan in the air blowing direction of the fan. The fan muffling system according to any one of claims 1 to 8, wherein the acoustic resonance structures are arranged upstream and downstream of the fan in the air blowing direction of the fan. 3. The acoustic resonance structure is a membrane-type resonance structure comprising a membrane having a fixed peripheral portion and supported so as to be able to vibrate the membrane, and a back space formed on one side of the membrane. 11. The fan muffling system according to any one of 1 to 10. 12. The fan muffling system according to claim 11, wherein the membrane-type resonance structure has a through-hole that communicates the back space with the outside. The fan noise reduction system according to any one of claims 1 to 12, wherein the fan is an axial fan.

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